Depends on how you work the decks...
It is not uncommon for EVERY ADAT to have at least a slightly different REW and FFWD speed.
This becomes an issue depending on how you work with the decks.
Example:
If the faster deck is the Master deck, if you are using the Loop function for a couple of locates, a lot of times, the Master deck will start playing right when it gets to it's start locate point, even though the slower deck is still rewinding or trying to get to the exact start locate. In this case, the Slave deck will have to try to catch up and achieve sync. This is hard on the transport.
In this case, I have found that it is better to make the slowest deck the Master and the faster ones Slaves. The Slave decks will get to the locate first, and wait for the Master deck to get there before they all start to play.
If you don't use loops then it really doesn't matter which deck is Master or Slave because figuratively, you would be waiting for all the decks to park at the locate point before you hit Play.
Hope this helps.
Ed